Field of the Invention
The present invention relates to an etched tubular device, particularly cylindrical, biocompatible medical devices for insertion into a body during medical procedures and to a method for manufacturing these devices. More particularly, the invention relates to flexible tubular devices for use as stents, catheters (including, for example, guide catheters and balloon catheters, guidewires, catheter sheaths, microcircuitry containing catheters, catheter introducers and drug infusion catheters/guidewires) and methods for making these devices.
Catheters and Guidewires
Catheters are relatively thin and flexible tubes used in the medical field for numerous applications. Catheters are made by any number of different methods and designs. However, in most catheter designs it is desirable to obtain a maximum torsional rigidity while retaining a satisfactory longitudinal flexibility and stiffness without kinking. These features allow the catheter to be manipulated so that the catheter can be guided through small body vessels and cavities. These features will also prevent any kiking from occurring, and provide the catheter with sufficient stiffness to prevent the catheter from wrinkling or folding back on itself during this process. The specific nature of these characteristics vary depending on the specific application for which the catheter is being used. Another consideration is that a relatively small outside diameter must be maintained while providing a lumen or an inside diameter as large as possible.
Guidewires require the same general type of physical characteristics. However, with guidewires it is important to minimize the outside diameter of the guidewire so that they will readily fit inside of the lumen of the catheter.
Catheters and guidewires are used both as diagnostic tools and therapeutic tools in the treatment of diseases. One such diagnostic procedure is cardiac catheterization which is a widely performed procedure, being used for assessment of coronary artery disease. Other uses are neurologic uses, radiologic uses, electrophysiologic uses, peripheral vascular uses, etc. Example of therapeutic uses are balloon catheterization in dilation procedures to treat coronary disease and retroperfusion delivery of drugs at targeted sites within the human body. Dilation procedures rely upon the use of a catheter for injection of contrast and delivery of guidewires and dilation catheters to the coronary artery or other arteries. An example of the use of guidewires is for Percutaneous Transluminal Coronary Angioplasty (PTCA) balloons and for guiding diagnostic catheters through the arteries and to body organs. Retroperfusion drug delivery requires the use of the catheter to guide a tube carrying the drug to be delivered, and in some cases to have the catheter determine part of the rate of perfusion by the size, number and distribution of openings in the catheter through which the drug will pass.
The catheters and guidewires used in these and other procedures must have excellent torque characteristics, and must have the requisite flexibility. In addition, it is important that catheters and guidewires provide sufficient longitudinal support for xe2x80x9cpushingxe2x80x9d of items through the arteries and other vessels such as when feeding the balloon portion of an angioplasty catheter through the arteries. Unless there is sufficient stiffness, the catheter or guidewire will wrinkle or fold back on itself
Typically, in the case of a catheter, the larger the ratio of inside to outside diameter, the better, even while striving for minimum outside diameters for the catheters. Smaller catheter and guidewire outside diameter sizes result in less chance of arterial damage.
Catheters and guidewires must have sufficient torque to reduce buckling when being manipulated. Additionally, flexibility is important so that the catheter or guidewire can be manipulated into the varying arterial branches encountered by the catheter. The guidewire must resist being inadvertently kinked, as this can result in loss of torque control.
Prior art catheters are typically made of flexible materials which are reinforced such that the resulting composite catheter approximates the desired characteristics. In alternative approaches, guidewires are used in conjunction with catheters to assist in manipulating and moving the catheters through the arterial system in the body.
Stents are small, expandable tubes, usually used for insertion into a blocked vessel (vein or artery or duct) or other bodily part. Their physical characteristics must often be the same as those for catheters, except for the fact that they also must be expandable. This expansiveness is effected, not by elastic expansion under pressure, as is the case with balloons or parachutes in surgical procedures, but by more spring-like, metal memory characteristics in the material. Stents are often formed of a metal tube which is compressed (without exceeding the elastic flexibility or stress of the metal), inserted, and then released to allow the stent to expand to its original size and shape.
U.S. Pat. No. 4,020,829 discloses a spring guidewire for use in catheterization of blood vessels. The guidewire is axially slidable within a thin-walled, flexible plastic catheter. The distal portion of the guidewire is of a relatively short length and is connected to a relatively long, manipulative section capable of transmitting rotational torque along its length. In this invention the catheter tube might be advanced over the guidewire after the guidewire has been properly positioned or the catheter might be advanced together with the guidewire, the guidewire providing a reinforcement for the thin wall of the catheter.
U.S. Pat. No. 4,764,324 discloses a method for making a catheter. A reinforcing member is heated and applied to a thermoplastic catheter body so as to become embedded in the wall of the catheter. The wall of the catheter is then smoothed and sized so as to produce a composite, reinforced catheter.
Current catheters often suffer from either problems of torque, size, flexibility, kinking, and poor support during PTCA in the case of guide catheters. Moreover, catheters cannot be readily made with variable stiffness along the length of the catheter.
Catheter Sheaths and Introducers
Catheter sheaths and introducers are used to provide a conduit for introducing catheters, fluids or other medical devices into blood vessels. A catheter introducer typically comprises a tubular catheter sheath, a hub attached to the proximal end of the sheath having hemostasis valve means to control bleeding and to prevent air embolisms, and a removable hollow dilator that is inserted through the hub, valve means and the lumen of the catheter sheath. Many catheter introducers also contain a feed tube that is connected to the hub to facilitate the introduction of fluids into the blood vessel.
Positioning an introducer into a blood vessel begins by inserting a hollow needle through the skin and into the lumen of the desired blood vessel. A guidewire is then passed through the needle and into the blood vessel. The needle is then removed leaving the guidewire in the vessel. Next, the sheath and dilator are advanced together over the guidewire until the distal ends of the dilator and sheath are positioned within the lumen of the vessel. The guidewire and dilator are then removed, leaving the distal end of the sheath within the vessel. Catheters or other medical devices can then be passed through the introducer and sheath into the desired vessel.
Conventional sheaths are made of plastic and are subject to kinking if bent without internal support. This kinking can occur during the insertion of the device or if the patient moves while the sheath is in the vessel. Unfortunately, this kinking can create sharp edges or irregularities in the sheath that can damage blood vessel linings. This kinking can also make the introduction of devices or fluids more difficult and can cause patient bleeding problems around the sheath tubing. Therefore, there arises a need for a catheter introducer with a catheter sheath that is flexible and resistant to kinking.
Drug Infusion Catheters/Guidewires
Drug infusion catheters/guidewires are devices that act like both catheters and guidewires and are capable of delivering drugs or other fluids to a specific location within a patient""s blood vessel such as an occluded blood vessel. The guidewire type devices are typically comprised of a coil spring with a heat-shrunk TEFLON(copyright) coating and a core wire that can be inserted and removed from the lumen in the coil spring. The coated coil also contains either side holes or an end hole or a combination thereof in its distal end to enable the drugs or other fluids to be sprayed into the blood vessel.
During use, the coated coil spring and its core wire are advanced together through the patient""s circulatory system much like conventional guidewires. Upon reaching the desired location, the core wire is removed creating a small catheter-like device. Drugs or other fluids are pumped through the lumen in the coated coiled spring, out of the holes and into the blood vessel at the desired location.
Because these devices act like guidewires, the outside diameter of the devices, and therefore the lumen, are limited in size. Therefore, a second type of drug infusion catheter/guidewire device utilizes a catheter-like member with side holes and a tapered distal end having an end hole generally equal to the outside diameter of a guidewire. These catheter-type drug infusion catheter/guidewire devices are advanced over a guidewire to the desired location and then drugs are then pumped through and out of the holes in the catheter-like member. These devices can also be used in combination with the guidewire-type drug infusion devices.
As described above, drug infusion catheter/guidewire devices act like both catheters and guidewires. Therefore, these devices must have the same characteristics as catheters and guidewires. These devices must obtain a maximum torsional rigidity while retaining a satisfactory longitudinal flexibility and stiffness without kinking. They must also maintain a small outside diameter while providing a lumen as large as possible.
Stents
Stents are devices that are placed into and/or implanted in the body, and in particular in body structures including vessels, tracts or ducts. For example, stents are commonly used in blood vessels, the urinary tract and in the bile duct, to treat these body structures when they have weakened. With blood vessels, stents are typically implanted therein to treat narrowings or occlusions caused by disease, to reinforce the vessel from collapse or to prevent the vessel from abnormally dilating, as with an aneurysm or the like.
Stents are typically produced at a first smaller diameter for deployment and then expanded to a larger diameter, upon placement into the body vessel, tract, duct or the like. Deployment of stents it typically achieved by mounting the stents on balloon catheters and then once at the requisite position in the body vessel, tract, or duct, expanding the stent to the larger diameter, for permanent placement therein. U.S. Pat. No. 4,856,516 to Hillstead discloses a typical stent and describes a method for its deployment and placement with a balloon catheter.
U.S. Pat. Nos. 5,649,952 and 5,603,721 describes an expandable stent, a method for implanting a stent in a patient and a method for making that type of stent. The stent comprises a cylindrical frame which has patterns of materials removed from the cylindrical mass formed of interconnected elements designed to expand evenly under radial stress. In a preferred structure, a serpentine pattern is formed aligned on a common longitudinal stent axis to form elements that expand evenly under radial stress and maximize the overall radial expansion ratio. Although no methods are claimed in the patent for manufacturing the elements, various methods of manufacture are described such as coating a thin walled tubular element with a material which is resistant to chemical etchant, removing patterns of the resist material to expose portions of the underlying tubular element, and subsequently etching to remove a pattern of the tubular material which will leave the designed pattern in the tubular element so that it has a pattern which provides the desired expandability. It is stated that it is preferred to apply the etchant resistant coating by electrophoretic deposition and to remove the etchant-resistant material by means of a machine-controlled laser.
U.S. Pat. No. 5,437,288 describes an apparatus for use as a catheter guidewire and a method for manufacturing a catheter guidewire. The apparatus for use as a guidewire comprises an elongate, non-coiled wire having a flexible portion located between a distal and a proximal end, the distal end (and distal portion) of the apparatus having spaced grooves cut therein. The claimed method of making the guidewire comprises providing a metal wire, cutting a plurality of axially spaced grooves in the metal wire, and increasing the depth of the grooves toward the distal tip to create a flexible portion. The grooves are suggested to be formed in the wire by any suitable machining method, such as grinding, electrostatic discharge machining (EDM), lasers or the like.
WO 97/42910 relates to a novel apertured flexible tubular member with an encasing for insertion into vessels of the body as part of a medical device. For example, the invention can be used as catheters, including guide catheters and balloon catheters, guidewires, catheter sheaths for use with catheter introducers, or drug infusion catheter/guidewires. These catheters also relate to novel apertured flexible tubular stents which may be coated, for insertion into vessels, tracts or ducts. One embodiment is coated with a low friction material such as a low friction polymer so as to provide for lubricity. Samples of materials that might be used are polyurethane, hydrogels, polyethylene, polytetrafluoroethylene (PTFE) and, in particular, one such material which might be used is TEFLON(copyright).
In some embodiments, such as catheters or sheaths, the inside of the flexible tubular member is also preferably coated with a low friction material such as hydrogel and/or with an anticoagulant such as heparin. Another embodiment uses slots of a predetermined configuration cut into a single, hollow, thin-walled metal tube at predetermined spacings, depth and pattern so as to provide the tube with a desired flexibility. The tube is then encased in a suitable low-friction material as noted above or some other suitable coating material. The method of forming the tubular member includes:
a) providing a tubular element including an outer surface;
b) providing a light source (including columnated light);
c) creating a pattern on the tubular element by:
1. applying a photoresistive material to at least a portion of the outer surface of said tubular element,
2. providing a mask intermediate the tubular element and the light source, at least a portion of the mask including a predetermined pattern formed of predetermined locations translucent to light from the light source,
3. activating the light source to expose a first area of the photoresistive material on the outer surface of the tubular element,
4. moving the tubular element such that at least a second area on the outer surface of said tubular element is substantially aligned with said at least a portion of the mask including predetermined locations translucent to light from the light source,
5. activating the light source to expose the second area of the photoresistive material on the outer surface of the tubular element, and
6. developing the photoresistive material on the tubular element, to create first portions and second portions of the photoresistive material, the first portions and the second portions corresponding to their respective exposure from the light source (including columnated light); and
d) removing segments of the tubular element corresponding to the first portions of the photoresistive material.
The mask is shown to include typical stencil-type masks, ink patterns (e.g., applied by a laser printer), and film masks, and either negative-acting or positive-acting resists can be used. Chemical etching of the tube is shown.
The present invention describes a method for providing a flexible cylindrical element, such as a medical stent, comprising the steps of providing a cylindrical body (e.g., a hollow cylindrical body), coating the cylindrical body with a photosensitive resist material (either positive or negative acting), exposing the photosensitive resist material to focused or coherent radiation to which the photoresist composition is sensitive, developing the exposed photosensitive resist material to a fluid developing environment which will selectively remove areas of the photoresist which are more soluble in the fluid developing environment, and then chemically etching exposed surfaces of the cylindrical element which has been exposed by the development of the photoresist coating. The residual photoresist material may be stripped, the patterned cylindrical element cleaned, inspected, packaged and sent to the end user.